There is a lot of activity going on at the Greens Creek Mine on Admiralty Island — construction, maintenance, exploration and a bit of thumb twiddling, too.

The mine plans its expansion in decade-long chunks, Scott Hartman, president and general manager of Hecla Greens Creek Mining Company, told the Juneau Chamber of Commerce on Thursday.

“We’ve been a 10-year mine for 23 years,” Hartman said. “We are investing many millions of dollars,” he said, “and that is for a 10-year mine life.”

One of its major current expansion projects, one that can encompass decades of growth, is to increase the area of the mine’s tailings storage. While the current site is not full yet, even the mine’s current reserves would create more tailings than the facility can handle, Hartman said. Not to mention the possibility the mine will continue to find new reserves, he said.

“There are no guarantees,” Hartman said. “But that is the nature of our business.”

The mine and its roads cover 350 acres.

About 21 percent of the ore removed from Greens Creek mine ends up as tailings in its dry stack tailings facility, Hartman said. Half of the ore tailings are used as backfill underground. The mine blends cement with tailings to fill in mined-out shafts. The process shores up the mine for further extraction.

The dangers associated with the disposal of mine tailings relate to their longevity and the tailings’ chemical reaction with surface and shallow subsurface water.

Water, mixing with sulfides in the crushed rock, creates an acid. This acidic water can leach heavy metals from the tailings.

“The resulting fluids may be highly toxic and, when mixed with groundwater, surface water and soil, may have harmful effects on humans, animals and plants,” according to an Environmental Protection Agency report.